Many countries have set up (or are soon going to set up) satellite constellations dedicated to localization in the GNSS (1.16 to 2.5 GHz) band. There are different GNSS systems, among them:                the GPS system for the USA        the GALILEO system for Europe        the GLONASS system for Russia        the COMPASS system for China, and        the IRNSS system for India.        
The GPS, GALILEO, GLONASS and COMPASS systems use frequencies ranging from the 1.164 to the 1.1602 GHz bands. By contrast, the IRNSS system uses frequencies in the band around 2.49 GHz.
The spectrum of frequencies used by the GNSS system is very broad. The antennas must therefore be capable of efficiently picking up signals from the different constellations in the band ranging from 1.16 to 2.5 GHz (more than one octave) with circular polarization and a directional radiation pattern.
The literature on the subject often refers to two types of antennas:                dual-band antennas to cover two bands (one band from 1.16 to 1.3 GHz and the other band from 1.55 to 1.61 GHz (see for example the patent document WO2007006773 entitled “Antenna multibandes pour système de positionnement par satellite” (Multi-band antenna for satellite positioning system); and        broadband antennas which generally cover the entire 1.16 to 1.61 GHz band (see for example Hong-Lin Zhang, Xiu-Yin Zhang, Bin-Jie Hu, “Compact broad-band annular ring antenna for global navigation satellite systems, 9th International Symposium on Antennas Propagation and EM Theory, Vol., No., pp. 189, 192, 29 Nov. 2010-2 Dec. 2010).        
One drawback of these two types of known antennas is that they do not cover the 2.5 GHz band. In other words, they do not cover the entire GNSS band (1.16 to 2.5 GHz).
There is also a third known type of antenna, namely antennas that are narrow-band antennas but are tunable on a very wide frequency band.
FIGS. 1A, 2A and 2B illustrate an example of an antenna of this third type, namely a slot-fed and frequency-tunable planar antenna 1. FIG. 1A is a three-quarter view, FIG. 2A is a top view and FIG. 2B is a view in section. This is an association between a planar antenna (also called a patch antenna) that is slot-fed and two variable capacitance elements 7 (in this example variable capacitance diodes also called varicap diodes). These diodes enable the antenna to be made tunable over a wide band of frequencies.
The slot-fed planar antenna possesses a structure in which the following are superimposed successively:                a resonant patch 1        a first dielectric layer 2 (for example consisting of air or a dielectric substrate)        a ground plane 3 comprising a slot 4 (operating according to single linear polarization in this example)        a second dielectric layer 5 (for example air or a dielectric substrate) and        a transmission line 6 (also called a feed line even if the antenna is used in reception) comprising an end strand extending beneath the slot.        
In the particular implementation illustrated, the first dielectric layer 2 is a layer of dielectric material with a thickness t and permittivity ∈r1, on the upper face of which the resonant patch 1 is printed. The second dielectric layer 5 is a layer of dielectric material with a thickness h and permittivity ∈r2, on the upper face of which there is printed the ground plane 3 (comprising the slot 6) and on the lower face of which there is printed the transmission line 6 (represented in dashes) and a continuous polarization line (used to convey the bias voltage to the resonant patch 1 which is itself connected to the variable capacitance elements 7).
Each variable capacitance element (varicap diode) is connected between a radiating side of the resonant patch 1 and the ground plane 3. The matching of the antenna varies according to a bias voltage applied to the variable capacitance elements.
FIG. 1B presents six curves illustrating the variation of the reflection coefficient S11 as a function of the frequency for different values of the bias voltage of the varicap diodes. Each curve corresponds to a distinct resonance and is obtained from one of the values of the bias voltage (0V, 4V, 8V, 12V, 16V and 22V). The matching of the antenna varies according to the bias voltage of the diode. The frequency of operation of the antenna varies between 1.7 GHz and 2.4 GHz, for a bias voltage that varies between 0 and 22V. This antenna is therefore tunable on a wide band of frequencies.
One major drawback of this antenna is that this tunability over a wide band of frequencies requires the use of very high bias voltage values which exceed 20V.